1. Field of the Invention
The present invention relates to a method of producing a ceramic multilayer substrate on which semiconductor LSI, a chip components, or the like are mounted and wired to each other.
2. Description of the Related Art
Japanese Unexamined Patent Publication No. 5-102666 discloses a conventional method of producing a ceramic multilayer substrate. According to this production method, as shown in FIG. 1, plural glass-ceramic green sheets made of a glass-ceramic, containing an organic binder and a plasticizer, and having a conductor pattern (not illustrated) formed on the surfaces thereof by use of a conductor paste composition are first laminated to form a laminate 101. Next, ceramic green sheets 102 and 103 containing as a major component an inorganic composition having a sintering temperature higher than that of the glass-ceramic green sheet 101 are formed on the back and front sides of the laminate 101, respectively, and thereafter, pressure-bonded together to form a lamination pressure-bonding body 100. Next, the lamination pressure-bonding body 100 is fired under the firing conditions for the laminate 101. Thereafter, the unsintered ceramic green sheets 102 and 103 are removed, whereby a ceramic multilayer substrate is obtained. The laminate 101 is inhibited from heat shrinking in the plane direction at firing, owing to the ceramic green sheets 102 and 103 of the lamination pressure-bonding body 100.
Such a conventional method of producing a ceramic multilayer substrate has the following problems.
When the number of the laminated glass-ceramic green sheets becomes large, and the thickness of the laminate 101 is increased, the vicinities of the ceramic green sheets 102 and 103, that is, the vicinities of the front and back sides of the laminate 101 are inhibited from heat shrinking in the plane direction. However, there have been some cases that the central portion 104 in the thickness direction of the laminate 101 is distorted so as to be depressed toward the inside thereof as shown in FIG. 2. There has been a danger that such distortion 104xe2x80x2 causes the inside of the laminate 101 to because cracked and the glass-ceramic green sheets to peel away from each other.
In the case that a cavity for accommodating an electronic component, not illustrated, is formed in the laminate 101, it has been difficult to provide a ceramic green sheet for inhibiting heat shrinkage on the bottom of the cavity.
To overcome the above described problems, preferred embodiments of the present invention provides a method of producing a ceramic multilayer substrate in which the side faces of the laminate can be prevented from being distorted so as to be depressed toward the inside thereof, caused by the heat shrinkage at firing. In addition, it is an object of the present invention to provide a method of producing a ceramic multilayer substrate in which an inorganic composition for inhibiting the heat shrinkage can be easily provided on the bottom of a cavity in the laminate.
One preferred embodiment of the present invention provides a method of producing a ceramic multilayer substrate by lamination of plural glass-ceramic green sheets made of a glass-ceramic containing an organic binder and a plasticizer to form a laminate, and firing of the laminate comprises the step of applying to or overlaying on the surfaces of the glass-ceramic green sheets inorganic compositions having a higher sintering temperature than the glass-ceramic green sheets, the step of laminating a plurality of the glass-ceramic green sheets having the inorganic compositions applied to or overlaid on the surfaces of the glass-ceramic green sheets to form a part of the laminate, and the step of laminating a plurality of the glass-ceramic green sheets to form the other part of the laminate.
The above described method may include the step of forming one of the glass-ceramic green sheets so as to have a smaller thickness than each of the other glass-ceramic green sheets, the step of applying to or overlaying on the surface of the glass-ceramic green sheet having a smaller thickness the inorganic composition, the step of arranging the glass-ceramic green sheet having a smaller thickness as the undermost layer of the laminate, and the step of laminating a plurality of the glass-ceramic green sheets having the inorganic compositions applied to or overlaid on the surfaces thereof, whereby a part of or the whole of the laminate ranging from the vicinity of the undermost layer to the uppermost layer is formed.
The above described method may include the step of laminating a plurality of the glass-ceramic green sheets having the inorganic compositions provided on the surfaces thereof, whereby a part of or the whole of the laminate ranging from the undermost layer to the vicinity of the uppermost layer is formed, and the step of laminating the glass-ceramic green sheet as the uppermost layer of the laminate.
Moreover, the method may include the step of forming the glass-ceramic green sheets to constitute the undermost and uppermost layers of the laminate so as to have a smaller thickness than the respective glass-ceramic green sheets to constitute the other layers of the laminate.
Further, the method may include the step of forming opening portions through a plurality of the glass-ceramic green sheets arranged as the uppermost layer of the laminate and in its vicinities and also the inorganic compositions applied to or overlaid on the glass-ceramic green sheets, and the step of laminating a plurality of the glass-ceramic green sheets having the opening portions formed therein to form the laminate having a cavity formed of the opening portions of the plural glass-ceramic green sheets which are made continuous to each other.
In the above described method, the inorganic compositions applied to or overlaid on the glass-ceramic green sheets may contain alumina as a major component.
Further, each of the inorganic compositions applied to or overlaid on the glass-ceramic green sheets may have a thickness of from about 1 to 20 xcexcm.
Furthermore, the differences between the sintering temperatures of the glass-ceramic green sheets and the sintering temperatures of the inorganic compositions applied to or overlaid on the glass-ceramic green sheets is at least about 100xc2x0 C.
Further, the above described method may include the step of forming a glass-ceramic green sheet on a carrier film, and then applying to or overlaying on the glass-ceramic green sheet the inorganic composition to form an inorganic composition layer, the step of forming a perforation through each of the carrier film, the glass-ceramic green sheet and the inorganic composition layer, filling a conductor material into the perforation to produce a viahole, and further forming a conductor pattern on the inorganic composition layer, and the step of releasing the glass-ceramic green sheet having the viahole and the conductor pattern, together with the inorganic composition layer, from the carrier film and laminating the glass-ceramic green sheets with the inorganic composition layers, sequentially.
Further, the method may include the step of applying to or overlaying on a carrier film the inorganic composition to form an inorganic composition layer, and then forming a glass-ceramic green sheet on the inorganic composition layer, the step of forming a perforation through each of the carrier film, the inorganic composition layer and the glass-ceramic green sheet, then filling a conductor material into the perforation to form a viahole, and forming a conductor pattern on the glass-ceramic green sheet, and the step of releasing the glass-ceramic green sheet having the viahole and the conductor pattern, together with the inorganic composition layer, from the carrier film and laminating the glass-ceramic green sheets with the inorganic composition layers sequentially.
Moreover, a glass-ceramic green sheet having a viahole and a conductor pattern and a green sheet having a perforation not filled with a conductor material, corresponding to the viahole and containing the inorganic composition as a major component may be laminated to form a part of the laminate.
According to the method of producing a ceramic multilayer substrate of the present invention, the glass-ceramic green sheets and the inorganic compositions having a higher sintering temperature than the respective glass-ceramic green sheets are alternately arranged to form a laminate, and fired. Owing to the inorganic compositions, the glass-ceramic green sheets constituting not only the undermost and uppermost layers of the laminate but also the internal layers are inhibited from heat shrinking in the plane direction. Accordingly, there is little danger that distortion of the laminate occurs at firing, that is, the side faces of the laminate are distorted so as to be depressed toward the inside. Therefore, the generation of cracks and the peeling of the glass-ceramic green sheets are prevented. The production of a high precision ceramic multilayer substrate is enabled.
By forming the undermost layer of the laminate, or the undermost and uppermost layers thereof with the glass-ceramic green sheets, the sintered glass-ceramics after the laminate is fired can be used as the mounting surfaces of the ceramic multilayer substrate. Accordingly, the mounting surfaces are stable, and the ceramic multilayer substrate can be mounted without fail as compared with the surfaces made of unsintered inorganic compositions.
By forming the glass-ceramic green sheets constituting the undermost or uppermost layer of the laminate or both of them so as to have a smaller thickness than the respective glass-ceramic green sheets constituting the other layers of the laminate, the amount of change caused by heat shrinkage of the respective layers can be made equal to each other. Accordingly, the peeling or the generation of cracks can be prevented from occurring between the glass-ceramic green sheets.
Further, the inorganic composition having a higher sintering temperature than the glass-ceramic green sheet is exposed on the bottom of the cavity formed in the laminate. Accordingly, it is unnecessary to provide an inorganic composition on the bottom of the cavity after the cavity is formed. The bottom of the cavity can be simply protected from heat shrinking at firing.
Since the inorganic compositions having a higher sintering temperature than the respective glass-ceramic green sheets are arranged inside of the laminate, the unsintered inorganic compositions function as a buffering material against vibration, impact and thermal shock. Accordingly, cracks or breaks fatal to the laminate are not generated.
Since the glass-ceramic green sheets constituting the laminate and the inorganic compositions for inhibiting the heat shrinkage at firing have different sintering temperatures, the co-firing of the whole laminate is possible, and the simplification of the manufacturing process and the reduction of the manufacturing cost can be realized.
In the case that the materials for use in the inorganic composition to inhibit the heat shrinkage include no glass, even though the conductor constituting the internal electrodes is diffused was firing of the laminate, caused by the plastic flow of the glass-ceramic green sheets, diffusion can be inhibited owing to the inorganic compositions for inhibiting the heat shrinkage.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.